The loss of the dopant in ultrashallow junction (USJ) by RCA standard clean (SC1) prior to the formation of side-wall spacer is quantified by using transmission electron microscopy (TEM), secondary ion mass spectroscopy, four-point probe, and source/drain extension (SDE) sheet-resistance test structure (SSTS). From the cross-sectional TEM images, the etched depth by one SC1 for n (p)-type SDE was measured to be 1.5 nm (0.2 nm). From the secondary ion mass spectroscopy profiles, most of the n-type dopant implanted with arsenic at 2 keV is expected to be etched-out by four times of SC1 cleaning, while the p-type dopants are immune to SC1 cleaning. We quantified the dopant loss from sheet resistance measurements with the four-point probe and the SSTS. The effect of SC1 cleaning on transistor performance is discussed in terms of on-state current. The dopant loss by SC1 is found to be the most significant factor in process optimization for n-type field effect transistor with USJ. (c) 2006 American Vacuum Society.